Friday, July 19, 2019 [Tweets] [Favorites]

Margaret Hamilton and Apollo 11

Margaret Hamilton (via Hacker News):

There were two onboard computers – one on the command module, Columbia, and one on the lunar module, Eagle. Our task included developing the software to run on each and the systems software they shared. At the beginning, nobody thought software was that big a deal. But then they began to realise how much they were relying on it. The group grew so there were approximately 100 software engineers on my team. Astronauts’ lives were at stake. Our software needed to be ultra-reliable and it needed to be able to detect an error and recover from it at any time during the mission. And it all had to fit on the hardware.


Just as the astronauts were about to land, the software’s priority displays interrupted them with alarms to warn there was an emergency, and that the computer was overloaded. I learned about it as it was happening, standing in the monitoring room at MIT. We pieced together afterwards what had happened, which was that a radar switch was in the wrong position and it was taking up processing power. It quickly became clear the software was not only informing everyone that there was a hardware-related problem but was compensating for it – restarting and re-establishing the highest priority tasks. The error detection and recovery mechanisms had come to the rescue. It was a total relief when they landed – both that the astronauts were safe, and that the software worked perfectly.


During the early days of Apollo, software was not taken as seriously as other engineering disciplines. Though in fact we had a complex system of systems, we weren’t getting credit for what was a legitimate field. It was out of desperation I came up with the term, to say: “Hey, we’re engineering too.” It was an ongoing joke for a long time. Then one day in a meeting, one of the most respected hardware gurus explained to everyone that he agreed with me. The process of building software should also be considered an engineering discipline, just like with hardware.


The entire Apollo 11 computer code is available on @github, and it’s incredible.

Don Eyles:

The Apollo 11 mission succeeded in landing on the moon despite two computer-related problems that affected the Lunar Module during the powered descent. An uncorrected problem in the rendezvous radar interface stole approximately 13% of the computer’s duty cycle, resulting in five program alarms and software restarts. In a less well-known problem, caused by erroneous data, the thrust of the LM’s descent engine fluctuated wildly because the throttle control algorithm was only marginally stable. The explanation of these problems provides an opportunity to describe the operating system of the Apollo flight computers and the lunar landing guidance software.

Jason Kottke:

With the 50th anniversary of the first crewed landing on the Moon fast approaching, I thought I’d share one of my favorite views of the Moon walk, a map of where Neil Armstrong and Buzz Aldrin walked on the Moon, superimposed over a baseball field (bigger). The Lunar Module is parked on the pitcher’s mound and you can see where the two astronauts walked, set up cameras, collected samples, and did experiments.

Graham Roberts:

50 yrs ago, Apollo 11 returned to Earth with rolls of film containing iconic images: a boot print on the moon, a wrinkled U.S. flag, and a portrait of Buzz Aldrin with Neil Armstrong. Today @nytimes offers a perspective like never before.

Our inspiration came from a map originally created by NASA in 1970 that pinpoints the location and direction of every photo taken during this first moonwalk.

@kartpat, an editor on the Immersive team, wrote a custom program to determine how the moonwalk photographs were oriented in space. For each photo, he calculated the height of the camera, its direction and tilt, and the field of view of the lens.

The result: you can stand where Neil Armstrong and Buzz Aldrin were standing when they took these historic photographs. This three-part interactive article uses real-time 3-D graphics and Augmented Reality to bring it all together.

Jeremy Deaton (via Paul Kafasis):

Though almost no one knew it at the time, the mission had nearly ended in disaster. It was spared only at the last minute by two canny meteorologists with access to a top-secret weather satellite.


The storm, with its towering clouds and powerful winds, threatened to tear apart the parachutes on the command module on its descent into the Pacific.


Update (2021-01-07): Jason Kottke:

On July 20, 1969, 50 years ago today, Neil Armstrong & Buzz Aldrin landed on the Moon and went for a little walk. For the 11th year in a row, you can watch the original CBS News coverage of Walter Cronkite reporting on the Moon landing and the first Moon walk on a small B&W television, synced to the present-day time. Just open this page in your browser today, July 20th, and the coverage will start playing at the proper time.

Ken Shirriff:

The software to land on the Moon was woven by hand into core rope memory: wire through a core for a 1 bit, around a core for a 0 bit. Apollo Guidance Computer’s ropes held 36K of 15-bit words and used the first amplifier integrated circuits.

Cara Giaimo:

So in 1964, when [Margaret Hamilton] saw an ad from the MIT Instrumentation Lab recruiting programmers to work on software for what would become the Apollo program, Hamilton jumped at the chance. Initially, she was assigned what was presumed to be a low-impact project, writing the code that would kick in if an unmanned mission aborted. The higher-ups were “so sure this wasn’t going to happen,” she says, that she actually named her program “Forget It.” (When one of these missions did abort, she found herself in high demand.)

Scottie Andrew and Katherine Dillinger:

On Thursday, Google unveiled a giant tribute to Hamilton in California’s Mojave Desert: More than 107,000 mirrors were positioned to reflect moonlight and form her image for one night.

Jen Fitzpatrick:

The tribute was created by positioning over 107,000 mirrors at the Ivanpah Solar Facility in the Mojave Desert to reflect the light of the moon, instead of the sun, like the mirrors normally do. The result is a 1.4-square-mile portrait of Margaret, bigger than New York’s Central Park.

Jason Kottke:

50 years ago, the Sony TC-50 cassette player and recorder accompanied the Apollo 11 crew to the Moon and back. Ten years later, the company came out with the Walkman, the first portable cassette player that struck a chord with consumers. In this video, Mat of Techmoan shows us the TC-50 and shows how similar it is to the later Walkman.

Jordan Merrick:

For the 50th anniversary of the moon landing, Todd Douglas Miller’s breathtaking film of the Apollo 11 mission that’s comprised entirely of archive footage is essential viewing for all mankind.

Alexis Gallagher:

Interesting article on the Apollo 11 guidance computer.

Ken Shirriff (via Hacker News):

We recently restored an Apollo Guidance Computer, the revolutionary computer that helped navigate to the Moon and land on its surface. At a time when most computers filled rooms, the Apollo Guidance Computer (AGC) took up just a cubic foot. This blog post discusses the small but complex switching power supplies that helped make the AGC compact enough to fit onboard the spacecraft.

1 Comment

There's an interesting series of videos on YouTube showing the restoration of an Apollo Guidance Computer to a functional state.

First video:

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